THE CELL. 



CYTOLOGY. 



THE unfertilized egg of the starfish is a good example of 

 a typical cell or egg. Other eggs as those of Cerebratulus, 

 the large jellyfish Aurelia, or tissue cells, if large, may serve 

 equally well. 



1. Form. Are the cells alike in shape and size? The 

 shape of a 'cell, if unconfined, is usually spherical, but in 

 tissues this form is modified by the pressure of adjacent 

 cells, or as a result of adaptations for some particular function. 



2. Structure. The essential elements of every cell are 

 cell protoplasm or cytoplasm, and nucleus. Is there a mem- 

 brane about the cell? Note the general appearance of the 

 cytoplasm. Is it granular, fibrillar, or alveolar? Is the 

 cytoplasm alike in all parts? In some eggs spheres or 

 granules of yolk are scattered through the cytoplasm. In 

 what portion of the cell is the nucleus located? Is this 

 position constant? Is there a membrane about the nucleus? 

 What is the character of the contents of the nucleus? If 

 the cell is stained note the granules, or flakes, within the 

 nucleus which stain more densely. These are spoken of as 

 the chromatin, the faintly stained, or unstained, material is 

 achromatin. Is the chromatin arranged in any definite way 

 as though on a framework? Within the nucleus is often 

 a rather large, deeply, staining spot, the nucleolus. Is it 

 in any constant place in the nucleus? 



3. Cell Division. This fundamental feature of living things 

 presents two rather distinct and definite aspects, namely, 



